July 12th, 2024: Limited Storm Activity Today and Tomorrow

 Synopsis

The 500mb anticyclone will shift east today and become anchored over the Four Corners through the weekend with brisk easterly flow aloft over Arizona. Even though mid level flow is relatively favorable, the lack of moisture and associated instability will limit storm activity and mainly remain confined to the higher terrain and near the International Border. It will still be quite hot across the lower deserts with temps between 100 and 110 degF across SE AZ and between 110 and 115 degF in South-Central and Southwestern AZ.



 Yesterday's Storms Summary


Quite the active afternoon/evening yesterday in Tucson with strong thunderstorms generating heavy rain, gusty winds, and isolated penny-sized hail. Storms initiated over the White Mountains and Mogollon Rim by early afternoon, and the combination of potent outflow boundaries and synoptic scale ascent (induced by an inverted trough) allowed organized clusters of storms to move through the Tucson vicinity by late afternoon/early evening. Isolated reports of wind damage to trees, power lines, and roof tiles in the Tucson vicinity yesterday via SPC Storm Reports.


SPC Storm Reports of Wind/Wind damage from yesterday.


The 12z and 15z WRF-HRRR runs yesterday performed exceptionally well with both runs accurately forecasting the timing, coverage, and relative intensity of storms. This most definitely reflects the benefit of a regional Convective Allowing Model (CAM)!


 

Current Conditions


The 500mb anticyclone is finally shifting east toward the Four Corners with mid level flow turning easterly over Arizona as shown by the SPC 500mb analysis this morning.


SPC 500mb analysis as of 9:00AM MST this morning.


Surface dew points in the mid 50s to mid 60s across extreme Southern Arizona (increasing from east to west) this morning due to yesterday's precipitation and moisture from the Gulf of California.


Surface observations as of 9:40AM MST courtesy of the NWS.


Even though dew points are on the higher side this morning, the 12z TUS sounding measured only around an inch of precipitable water.

12z TUS sounding this morning courtesy of the SPC.


The surface moisture is underneath a strong nocturnal inversion with a dry layer above 850mb. There is around 600 J/kg of CAPE but -600 J/kg of CIN.


 


Today's Forecast


The 500mb anticyclone will continue to shift east toward the Four Corners throughout the day with brisk easterly mid level flow over AZ. Unlike yesterday, there isn't a synoptic scale mechanism to aid convective initiation and coverage. So overall the synoptic upper air pattern will have somewhat of a neutral influence on convection today.


As shown in the 12z TUS sounding this morning, precipitable water is only around an inch (slightly less than yesterday), and the surface dew points will plummet as surface heating will mix out the boundary layer. The 12z KTUS WRF-HRRR sounding forecasting a textbook inverted-V sounding this afternoon with CAPE well below 100J/kg.


12z KTUS WRF-HRRR sounding for this afternoon at 5:00PM MST.


In addition, CAMs forecasting a diurnally-driven pressure gradient to develop between the thermal low over the Lower Colorado River Valley and a surface high over western Texas by this afternoon. In response, CAMs forecast brisk 10 to 20 knot easterly winds to develop in SE AZ which will advect dry air from the east into the region this afternoon. CAMs forecast a surface convergence boundary to develop between the drier easterly flow and moist, westerly flow (induced by the Gulf of CA) in Central Pima County near the International Border.


12z WRF-HRRR 2-meter dew points and 10-meter wind barbs for this evening at 6:00PM MST.


This surface convergence boundary could act as a lifting mechanism for storms in that region. CAMs aren't very bullish with storm coverage though with the 12z WRF-HRRR forecasting only a few isolated cells near the Border late this afternoon.


12z WRF-HRRR simulated reflectivity for this afternoon at 4:30PM MST.


Other than that, it will remain mostly dry across Southern AZ with only an isolated cell or two possible over the highest peaks of the Sky Islands. 


On the other hand, expecting an active day over the higher terrain of Northern AZ with storm clusters expected to develop near Flagstaff and move east toward Nevada throughout the afternoon and early evening. Any storms that develop will have the potential to produce gusty winds, brief heavy rain, and small hail.


Unfortunately, it will be hot again across the lower deserts with high temps between 100 and 110 degF in SE AZ and between 110 degF and 115 degF in the lower deserts of South-central and Southwestern AZ. It will be a few degrees cooler near Yuma due to low level moisture hanging around into the afternoon.


12z WRF-HRRR 2-meter temps for this afternoon at 4:00PM MST.


Tomorrow's Forecast


CAMs forecast another Gulf of CA moisture surge overnight tonight with dew points increasing in the mid 50s to low 60s in the lower deserts from Tucson westward.


12z WRF-HRRR 2-meter dew points for tonight at 11:30PM MST.


The synoptics will be near identical tomorrow with the only change being the 500mb anticyclone centered over the Four Corners and mid level flow becoming easterly/southeasterly over AZ.


12z GFS 500mb cyclonic vorticity for tomorrow at 11:00AM MST courtesy of Tropical Tidbits.

 

CAMs forecast a near rinse and repeat surface pattern tomorrow with a diurnally driven pressure gradient developing between the thermal low in the lower Colorado River Valley and a surface high in Western Texas. CAMs forecast dry, 10 to 20 knot easterly winds to develop in SE AZ with dry air advecting into the region. This will likely suppress convection in SE AZ again tomorrow and potentially develop another surface convergence boundary in Central Pima County.


12z WRF-HRRR 2-meter dew points for tomorrow at 4:00PM MST.


Expecting storms to develop in the same areas tomorrow which would be over the higher terrain of Northern AZ and a few cells near the International Border.


12z WRF-HRRR simulated reflectivity for tomorrow afternoon at 3:00PM MST.


In general, expect today and tomorrow to be "down days" with storms remaining confined to the higher terrain of Northern AZ and near the International Border. Confidence is increasing that Sunday could be a very active day across the state and will provide more details in tomorrow's discussion. Stay tuned!








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